A wide variety of processes use radial flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Radial flow reactors are constructed such that the reactor has an annular structure and that there are annular distribution and collection devices. The devices for distribution and collection typically incorporate some type of screened surface. The screened surface is for holding catalyst beds in place and for aiding in the distribution of pressure over the surface of the reactor to facilitate radial flow through the reactor bed. The screen can be a mesh, either wire or other material, or a punched plate. For either a fixed bed or moving bed, the screen or mesh provides a barrier to prevent the loss of solid catalyst particles while allowing fluid to flow through the bed. In a moving bed, solid catalyst particles are added at the top and flow through the apparatus and are removed at the bottom, while passing through a screened-in enclosure that permits the flow of fluid over the catalyst. In a fixed bed, the catalyst, or adsorbent, is loaded into a bed between screens, or other retention devices, and the screens allow fluid to flow over the catalyst while holding the catalyst in place. The screen is preferably constructed of a non-reactive material, but in reality the screen often undergoes some reaction through corrosion and/or erosion, and over time problems arise from the corroded or eroded screen or mesh.
One type of screen is a profile wire screen, where a profile wire is wrapped around supports and set at a predetermined spacing for the wire as it is wrapped around the supports. The screen is then cut and flattened and then re-rolled or re-shaped. The screen is shown in U.S. Pat. No. 2,046,458 and U.S. Pat. No. 4,276,265. When flattened, the screen includes the profile wires, which are typically oriented vertically with support rods attached thereto and extending across the profile wires and orthogonally therefrom. The screen can be used as part of an inlet distribution device, or other device for containing a catalyst. One type of inlet distribution device is a reactor internal having a scallop shape and is described in U.S. Pat. No. 6,224,838 and U.S. Pat. No. 5,366,704. The scallop shape and design provides for good distribution of gas for the inlet of a radial flow reactor, but uses screens or meshes to prevent the passage of solids. The scallop shape is convenient because it allows for easy placement in a reactor without concern regarding the curvature of the vessel wall. The screens or meshes used to hold the catalyst particles within a bed are sized to have apertures sufficiently small that the particles cannot pass through.
In one common approach, profile wire screen(s) are formed into a generally tubular or cylindrical shape extending vertically within the generally vertical annular reactor about a central axis thereof. A perforated plate may be spaced from the profile wires and connected to opposite edges of the support rods on a fluid side of the screen within the reactor, while the profile wires are typically oriented on a material side. The plates are also formed or oriented to into a tubular or cylindrical shape within the reactor. Depending on the type of reactor and where within the reactor the screens are positioned, plates may be closer to the center or the outer walls of the reactor. As mentioned, the plates often include punched or perforated plates having a plurality of openings. The support rods are oriented above and below the openings and provide a channel for fluid to flow from the openings in the plate to the openings or mesh in the profile wire screens to provide good distribution of the fluid to the solid catalyst or adsorbent bed. In one design, the reactor includes a centerpipe that includes an inner annular plate and an outer annular profile wire screen as described. Fluid flows from an inlet through the centerpipe and passes through the plate openings and out of the screen to contact the catalyst.
It has recently been identified that the fluid flowing through the plate openings and channels can cause jetting which, when contacting the screen and the solid material on the opposite side of the screen, may cause vibration of the screen and/or solid material and accelerate corrosion or erosion of the outer surface of the profile wire screen and potentially damage the solid material. This can decrease the life of the equipment and catalyst or adsorbent within the reactor, increasing the cost of maintaining the reactor as well as down time required for changing out internal components of the reactor.
The design of reactors to overcome these limitations can save significantly on downtime for repairs and on the loss of catalyst, which is a significant portion of the cost of processing hydrocarbons.